In the past, as an exhaust gas purification catalyst arranged in an exhaust passage of an internal combustion engine, there has been known an NOx storage reduction catalyst (hereinafter, may be referred to as an “NSR catalyst”) which has an NOx reduction function to store nitrogen oxides (NOx) in exhaust gas and to reduce the NOx thus stored. This NSR catalyst also has an HC oxidation function to oxidize hydrocarbon (HC) in the exhaust gas.
In patent literature 1, there is disclosed an NSR catalyst having a two-layer structure in which a catalyst coat layer supported by a carrier includes a lower layer formed on a carrier surface and an upper layer formed on a surface of the lower layer. In the NSR catalyst disclosed in this first patent literature, at least one of platinum (pt) and palladium (Pd) is supported or carried by at least the upper layer of the catalyst coat layer. In addition, in the catalyst coat layer, a larger amount of rhodium (Rh) is supported by the lower layer than by the upper layer.